1. Field of the Invention
The present invention relates to a heat sink. More particularly, the present invention relates to a heat sink used for cooling an integrated circuit package, which generates heat, such as a microprocessor unit (MPU) incorporated into electronic equipment.
2. Description of the Related Art
Recently, concerning the integrated circuits used for a personal computer, especially concerning the MPU, the degree of integration is enhanced so as to enhance the function of the integrated circuit and increase the processing speed. Therefore, the quantity of heat generated in the integrated circuit has been increased. Accordingly, the inside of the casing of a personal computer is forcibly cooled by a cooling fan, and the MPU is located at a position where the cool air of the cooling fan flows, and a heat sink provided with a large number of fins is fixed to the MPU so that the MPU can be forcibly air-cooled. However, an MPU of a higher performance is now required for a personal computer. An MPU of a higher performance generates a quantity of heat larger than that generated by other electronic parts. For this reason, there is used a heat sink into which a cooling fan is incorporated so that an MPU, which generates a large quantity of heat, can be locally cooled by means of forcible air cooling. Such a heat sink into which a cooling fan is incorporated as a local cooling means is used to replace a conventional heat sink into which a cooling fan is not incorporated. Accordingly, there is proposed a heat sink of small size in which the cooling fan or a portion of the cooling fan is incorporated inside the cooling fins.
FIGS. 15A-C are views showing a heat sink described in Japanese Unexamined Patent Publication No. 62-49700 which is used as a local cooling means. FIG. 15A is a plan view which is taken from the upper surface side, FIG. 15B is a cross-sectional view taken at the one-dotted chain line ABCD shown in FIG. 15A, and FIG. 15C is a plan view taken in the direction of arrow Z in FIG. 15B. As shown in FIGS. 15A and 15B, this heat sink is composed in such a manner that a motor 2a, which is a drive section for blades 2b, is attached to the main body 1 of the heat sink, and fins 1a are perpendicularly arranged so that they surround the blades 2b. As shown in FIGS. 15B and 15C, the main body 1 of the heat sink is fixed to a heating element 3 such as a power transistor. Heat generated in the heating element is conducted to a bottom portion of the main body of the heat sink and further conducted to the fins 1a. When the motor 2a is driven, the blades 2b are rotated, so that cooling air is sucked from an upper portion of the cooling fan 2. The cooling air to which a centrifugal force is given by the rotation of the blades 2b cools the upper portions of the fins 1a, and the cooling air blown out downward by the blades 2b cools lower portions of the fins 1a. In this way, the cooling air which has been sucked from the upper portion passes through the fins 1a is discharged into the periphery of the heat sink. Therefore, the main body 1 of the heat sink can be cooled and further the heating element 3 can be cooled.
FIG. 16 is a view showing the heat sink described in Japanese Unexamined Patent Publication (PCT route) No. 8-502804. In the overall periphery of the main body 1 of the heat sink, there are provided a plurality of perpendicular fins 1a, and the cooling fan 2 is supported by the main body 1 of the heat sink. When the motor is arranged inside the blades 2b, the height of the cooling fan 2 in the axial direction is reduced, and when a portion of the cooling fan 2 intrudes into the main body of the heat sink, the thickness of the fan body 5 is reduced. When the cooling fan 2 is driven, the blades 2b are rotated, so that a cooling air can be sucked from the upper portion. The thus sucked cooling air cools the bottom portion of the main body 1 of the heat sink and passes through among the fins 1a. Therefore, the cooling air absorbs the heat which has been conducted from the main body 1 of the heat sink to the fins 1a, and the absorbed heat is dissipated to the periphery of the heat sink. When this heat sink is fixed to a heating element such as an MPU, the heating element can be locally cooled.
FIG. 17A and 17B are views showing the heat sink described in Japanese Unexamined Patent Publication No. 6-268125. FIG. 17A is a plan view which is taken from the upper surface. FIG. 17B is a cross-sectional view taken on line B--B in FIG. 17A. The motor 2a of the cooling fan 2 is fixed to the bottom portion of the main body 1 of the heat sink, and cooling fins 1a are perpendicularly arranged in such a manner that they surround the cooling fan 2. The bottom portion of the main body 1 of the thus composed heat sink is fixed to a heating element 3 such as an MPU. When the motor 2a is driven, the blades 2b are rotated, so that a cooling air can be sucked from the upper portion. The sucked cooling air passes through among the fins 1a and discharges into the periphery of the heat sink. When the fins 1a are cooled, the heating element 3 can be cooled via the main body 1 of the heat sink.
In the heat sinks shown in FIGS. 15A-C and 17A and 17B, the motor 2a which drives the cooling fan 2 is directly fixed to the bottom portion of the main body 1 of the heat sink. In the driving section of the cooling fan 2, ball bearings or sleeve bearings are used, and lubricant such as grease or oil is charged in the bearing. Due to the above structure, heat is directly transmitted to the bearing from the bottom portion of the main body 1 of the heat sink located close to the heating element 3. Accordingly, the temperature of the bearing is raised. When the temperature of the bearing is raised, the deterioration of the grease or oil is facilitated, and the life of the motor 2a is shortened.
In the heat sink shown in FIG. 16, the cooling fan 2 is mounted on the upper portion. Accordingly, areas of the fins 1a arranged on the side are small. Therefore, in order to realize a sufficiently high cooling performance, it is necessary to provide small fins with very small intervals between the fins. In order to realize the small fins 1a, the manufacturing cost is increased in the cutting process. Further, since the intervals between the fins 1a are very small, blocking tends to occur when dust gathers between the fins 1a. Accordingly, a quantity of cooling air is lowered, and the cooling performance is deteriorated.
In the structure of the heat sinks shown in FIGS. 15A-C and 17A and 17B in which the fins 1a are perpendicularly arranged on the overall bottom surface of the main body 1 of the heat sink, analysis of the flow of the cooling air becomes complicated and also analysis of the noise becomes complicated. Therefore, it is difficult to design the heat sink. Accordingly, it is impossible to optimize the cooling performance and reduce the noise.